The long-term goal of this research is to understand the neuroendocrine basis of behavior used in communication. The birdsong system is a valuable model because song is learned, and its neural circuits are sexually dimorphic, hormone sensitive, and plastic in adults. Seasonal plasticity of the song control system provides an especially interesting model of plasticity in vertebrate brains, and a continuing goal of this research program is to understand the mechanisms and functional consequences of these seasonal changes. The immediate goal of this application is to receive training in methods of molecular biology that will enable the candidate to extend his studies of plasticity of the song system to a molecular level of analysis. Brenowitz will learn gene cloning, mapping and targeting, single and double-label in situ hybridization, PCR, and nonviral cRNA transfection methods in the laboratory of Robert Steiner at the University of Washington (UW). The candidate will be trained by Paul Neiman of the Fred Hutchison Cancer Research Center in Seattle in the use of eDNA microarrays to analyze patterns of gene expression, and in bioinformatic methods for data analysis. Brenowitz will take a course on microarray analysis at the UW Center for Expression Arrays. Scott Edwards of UW will train Brenowitz in DNA sequencing methods. The candidate will "apprentice" at the Institute for Systems Biology in Seattle to learn current methods of proteomics and bioinformatics. UW has a strong research program, with particular strengths in birdsong, endocrinology, neuroscience, molecular biology, animal behavior, and hearing research. The candidate's appointments in the Depts. of Psychology, Zoology, and the Bloedet Hearing Research Center provide access to shared facilities that benefit his research program. The proposed research will address mechanisms and functional consequences of seasonal plasticity in the song system. Aims 1 & 2, will test the hypotheses that social enhancement of seasonal growth is mediated by auditory cues and involves increased neuronal recruitment. Aim 3 will test the hypothesis that afferent innervation is necessary to maintain seasonally grown song nuclei. Aim 4 will test the hypothesis that seasonal growth of song circuits is mediated by estrogenic metabolites of testosterone. Aim 5 will use operant conditioning to test the hypothesis that seasonal plasticity of the song nuclei causes seasonal changes in song perception. Aim 6 will use in situ hybridization to test the hypothesis that expression of the gene for brain derived neurotrophic factor is upregulated when the song circuits are seasonally growing. Aim 7 will use subtractive suppressive hybridization to identify genes that are enriched in a song nucleus that grows seasonally compared with a nucleus that does not grow. Aim 8 will use a customized eDNA microarray to analyze global patterns of gene expression that are associated with seasonal growth of the telencephalic song control circuits. The results of the proposed studies will increase our understanding of the influences of steroid hormones and social stimuli on the nervous system, and the relationship between plasticity in the adult brain and learning.